Wireless communication systems are widely deployed to provide mobile devices with various contents, such as voice, text, image, and moving pictures. For example, multiple channel access techniques allow multiple users to share system resources, such as bandwidth and transmission power. Examples of multiple channel access techniques include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, or orthogonal frequency division multiple access (OFDMA) systems. Such multiple channel access techniques can simultaneously support communication between multiple mobile devices.